drm/amd/include:cleanup vega10 athub header files.

Cleanup asic_reg/vega10/ATHUB folder,remove unused files.

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>